1. Field of the Invention
The present invention is related generally to a preconditioning apparatus for mixing and hydrating farinaceous materials such as flours, soy products, and the like. More specifically, the present invention is related to a preconditioner for mixing materials such as those commonly used in breakfast cereals, snacks, and pet foods, the preconditioner having an elongate receptacle comprised of two substantially cylindrical intercommunicated chambers, each chamber having a shaft extending longitudinally through the chamber, the shafts having beaters thereon for mixing the feed material and advancing it from an inlet end of the preconditioner to an outlet end of the preconditioner. More specifically, the shafts co-rotate and the beaters are oriented on the shafts in a way to increase product shear, interference, and retention time within the preconditioning apparatus for providing thorough mixing and conditioning of materials.
2. Description of the Related Art
Preconditioners are widely known for mixing feed materials with injected steam or water prior to extrusion, pelleting, or other processing of the material. In general, a preconditioner includes an enclosed chamber having a rotating shaft extending through the chamber. Beaters extend from the rotating shaft for mixing the feed materials. Early preconditioners were single shaft models having an enclosed cylinder with a rotating shaft down the central axis. Beaters on the rotating shaft mixed the feed material while advancing it from an inlet end of the preconditioner to an outlet end.
More recent, conventional preconditioners include two side-by-side intercommunicated mixing chambers. Each cylindrical chamber is of substantially equal diameter and is provided with a counter-rotating shaft having radially extending beaters positioned thereon. In other words, one shaft rotates in a clockwise direction while the other shaft rotates in a counterclockwise direction. Feed materials introduced into the preconditioner are mixed by agitation resulting from the rotating beaters.
Attempts have been made to improve mixing through the dual shaft preconditioning devices. For instance, U.S. Pat. No. 4,752,139 discloses a preconditioner having a first chamber, large in diameter, including a rotating shaft with beaters for advancing products from the inlet to the outlet of the preconditioner and a second chamber, smaller in diameter, having a shaft rotating in the opposite direction from the shaft in the first chamber. The shaft in the smaller chamber rotates faster than the shaft in the larger chamber.
Various problems associated with preconditioning have not been resolved by prior art devices. The primary objectives of a preconditioner are to evenly mix and properly condition materials introduced into the preconditioner. While providing rapidly rotating beaters enhances mixture of the materials, it has the negative effect of advancing the materials too rapidly through the preconditioner, thereby preventing sufficient conditioning with liquid or steam. In contrast, providing slowly rotating beaters increases the retention time of the products in the conditioner, and therefore allows more sufficient time for the materials to be introduced to steam and fluids, but does not as sufficiently mix and agitate the materials, in addition to perhaps taking longer than desired for conventional, industrial purposes. Furthermore, the flours and other materials being mixed tend to accumulate on slowly rotating beaters, thereby reducing their effectiveness and the overall efficiency of the preconditioner.
Furthermore, a device as disclosed in the U.S. Pat. No. 4,752,139, described above, requires excessively complicated and expensive hardware. Additionally, since the shafts in such a device rotate at different speeds and in opposite directions, and furthermore are located in different sized chambers, materials introduced into such a preconditioner are not retained for even amounts of time. Accordingly, the resulting conditioned material is inconsistent and may not be completely, thoroughly mixed.
Accordingly, the need exists for an inexpensive, dual shaft preconditioner that is easy to manufacture. Additionally, there is a great need for such a preconditioner which provides substantially consistent product retention time for all materials introduced into the preconditioner. Additionally, the need exists for a preconditioner that can thoroughly and evenly mix and condition the materials introduced therein. The present invention fills these and other needs.